113 research outputs found
Enhancing the Efficiency in Solar Systems: Time-Variant Modelling and Ray Tracing with Reference to Solar Energy Conversion Technologies in Concentration and Photovoltaic Systems
No full textThis thesis aims to present the research conducted during the Ph.D. period comprehensively. As the title suggests, the work encompassed various aspects related to the overarching theme of solar energy and modelling, characterized as a holistic investigation into diverse practical issues concerning solar energy.
The first part of the thesis introduces the 3D raytracing model FresnelSim, developed and refined throughout the Ph.D. program from previous research activities by the same author and research group. This model specializes in simulating and parametrically analyzing linear Fresnel solar systems. The simulation algorithm, implemented in Matlab, was validated against results from the open-source software Tonatiuh, a prominent tool for raytracing analyses. Following a presentation of the constitutive relationships and key equations governing raytracing, parametric analyses are presented focusing on optimizing geometric design parameters to maximize energy available to the receiver and/or to the heat transfer fluid flowing into an evacuated tube; these analyses include investigations into real plant geometries, notably those in Ben Guerir, Morocco, and Partanna, Italy. Another aspect examined is the impact on plant productivity due to orientations different from the optimal north-south alignment: notably, it is well-known that higher annual peaks can be achieved with plant orientations aligned along the north-south axis, while comprehensive analyses on the implications of alternative orientations, which are often necessitated by space constraints, are lacking in the literature. Additionally, leveraging the computational capabilities of FresnelSim, a new correlation for analytically calculating the Incidence Angle Modifier is proposed, departing from the conventional factored relationship, which often happens to be inaccurate.
A second research thread concerns the estimation of optimal tilt angles for photovoltaic modules to maximize their annual productivity. The mathematical model that was developed integrates geographic and climate considerations to establish correlations between these parameters and the best tilt and has been applied to case-study locations in France and Italy. Particularly, while real-world applications often employ a tilt angle equal to latitude, possibly decreased by 5°-10°, the optimal value is contingent upon deviations from ideal clear sky conditions: after the identification of such dependencies and computation of optimal angles for over 200 locations, an analytical equation is derived for tilt angle calculation across ideally both national territories. Furthermore, for a comprehensive analysis, distinct coefficients were identified based on the orientation angle of the capturing surface, yielding multiple angle sets for non-South facing surfaces. The same approach, which accounts for both isotropic and anisotropic diffuse insolation relationships, has been also applied to a set of Canadian cities with the aim of identifying the best tilts across the country and comparing results with those from available online resources with reference to locations characterized by completely different climate conditions with respect to the European ones.
A third aspect herein addressed involves the integration energy systems, including photovoltaic ones and thermal storages, into urban settings. A model was developed for a sensible heat thermal storage system to be integrated into the existing smart grid at the University of Genova campus located in Savona, Italy: based on a stepped two-zone approach, the model was embedded within the broader Energy Management System of the grid, allowing the optimization of storage tank size considering economic parameters as well as greenhouse gas reductions associated to the thermal storage beneficial effect. Input data for the analysis are based on 2-year records of thermal and electrical loads and photovoltaic energy production. A further research topic is the study of the photovoltaic potential of Genova rooftops: to assess the number and area of available surfaces for photovoltaic installations within the urban environment, a GIS-based 3D model of the built environment has been developed including proper hourly solar energy availability. The solar yield analysis has been carried out by building a cumulative 3D tiled sky to identify the most profitable surfaces in terms of size and expected annual insolation and near and far obstacles have been taken in consideration. Statistical processing of a reduced number of suburbs' rooftop surfaces have been calculated concerning their dimensions and reasonable insolation thresholds for considering profitable photovoltaic installation.
Lastly, during the Ph.D. period, a model was developed for predicting temperature and relative humidity parameters in an underwater greenhouse as part of the Nemo Garden® project. Although not directly aimed at energy production, this activity incorporates solar energy considerations in the model’s governing energy balance equations: indeed, the analytical model, which accounts for attenuated insolation due to the water column overlying the greenhouses, was validated against available measurements for a real installation in Noli, Italy, demonstrating high accuracy in estimating the aforementioned parameters of interest
Maximum energy yield of PV surfaces in France and Italy from climate based equations for optimum tilt at different azimuth angles
No full textIn the present paper, the problem of the determination of yearly maximum energy producibility in terms of optimum tilt angle for solar surfaces is addressed with reference to 216 locations in France and Italy. Original correlations are proposed to calculate the optimal surface slope as a correction parameter to be applied to the local latitude angle. The correction factor formulas are based on local climate conditions and have been inferred from local monthly insolation data (12-year global and diffuse irradiance, PV-GIS-SARAH platform). An optimization problem is solved aimed at maximizing the yearly collectable energy by a sloped surface, in a range of azimuth values (from South Facing to East Facing), for all the selected locations. Different equation forms have been investigated and compact and accurate formulas have been developed able to provide the optimal tilt as a function of latitude, surface azimuth and clearness parameters. The accuracy of the proposed formulas resulted in a correlation coefficient with respect to the "exact" tilt angles higher than 0.93 for azimuth angles till 60 degrees. Proposed formulas allow up to a 4% increase in collectable solar energy, corresponding, as an example, to a virtual increase in PV module efficiency from 21% to 21.8%
Ray tracing analysis of linear Fresnel concentrators and the effect of plant azimuth on their optical efficiency
No full textAlthough for a quite small number of installations, Linear Fresnel Collectors (LFC) represent an interesting technology for efficient solar energy exploitation at medium to high temperatures thanks to their lowest land area per electric power ratio if compared to other available CSP solutions. The first prototypes were realized in the '60 by Professor Giovanni Francia at the University of Genova, Italy. In this research, 3D ray tracing simulations are performed employing the proprietary, literature-validated code FresnelSim. This in-house developed algorithm, which models the effect of shading, blocking and end effects based on the plant geometrical parameters, has been implemented to efficiently describe plants whose axis is oriented differently than north-south, as it is often assumed. Based on different optical efficiency definitions and real plant dimensions and parameters, a parametric analysis is here presented to investigate the effect of the plant orientation on its performance. The energy available at the receiver results to be reduced by 8.7% on a yearly basis when the system is oriented eastwest instead of north-south; on the other hand, it has been observed that higher winter peak efficiencies and a more constant yearly production are achieved when the system is rotated with respect to the reference alignment
Linear Fresnel Ray Tracing Analysis: Southern Italy Plant Optimization Through FresnelSim Algorithm : An Analysis of the Main Design Parameters of the Primary Concentrator and an Insight on Compound Parabolic Collector Effectiveness
No full textThe goal of maximizing the optical efficiency of a Linear Fresnel Collector is typically addressed through Monte Carlo Ray Tracing simulations. This study introduces FresnelSim, a 3D ray tracing software developed at the University of Genoa, Italy, for the optical analysis of Linear Fresnel Collectors. FresnelSim has been herein used to examine key geometric factors and their impact on a reference plant's producibility, allowing to almost triple the irradiance at the secondary concentrator with respect to a reference base configuration. Through a series of fast parametric simulations, an optimized geometry for such a system is proposed, highlighting to which extent different efficiency indicators are dependent on mirrors’ gap, field length and mirrors’ radius of curvature. Then, an assessment of the effect of the plant’s azimuthal orientation in the range from 0° to 45° is presented, showing that the site’s yearly average producibility is reduced up to 3.3% as an effect of primary mirror alignment. Finally, an analysis of the Compound Parabolic Collector is presented in terms of sub hourly opto-energy efficiency for 3 reference days, resulting in values ranging from 80.9% to 87.4%. Energy flux circumferential uniformity at the absorber tube is evaluated under 6 different incidence angles, highlighting that irradiance uniformity could be further enhanced by a properly defined mirrors’ motion law
Best tilt of PV system in Canada: Effect of the sky radiation model and climate conditions
No full textThis paper focuses on the best tilt angle of photovoltaic applications, to be related to the latitude and a latitude correction factor here presented. The analysis includes a series of 19 cities across Canada: latitude and local weather conditions are considered to define a correction angle correlation. This correction is expressed as a function of latitude, average annual weather conditions, and yearly climate variability, demonstrating strong alignment with “exact” outputs (correlation coefficient equal to 0.98 for different sky models). To ensure broad geographic coverage, Typical Meteorological Year hourly data were obtained from the Canadian Weather Year for Energy Calculation portal. The validity of the correction was assessed against various approaches and web tools results. Results were then compared with those from European cities at similar latitudes. Findings indicate that determining the optimum tilt angle requires accounting for latitude and site-specific climatic conditions, including snow cover: snowy regions benefit from higher tilts, emphasizing the relevance of considering accurate albedo in photovoltaic system design. Results suggest that this precise tilt calculation can yield annual insolation gains of up to 3.5 % with respect to rule-of-thumb angles (i.e. tilt equal to latitude), even at lower latitudes, with variations in best tilts until 13°
Sky radiance distribution based model for rear and front insolation estimation on PV bifacial modules
No full textAnalysis of Thermo-Hygrometric Conditions of an Innovative Underwater Greenhouse
No full textNemo’s Garden® Project aims at creating a green, alternative, and original agriculture system based on underwater greenhouses (biospheres) developed for areas where plant growth is difficult in the terrestrial environment due to climate conditions and new global warming issues. Experiments were designed and performed to measure the thermal and hygrometric behaviour inside the biosphere; a simple theoretical model was developed to analyse the temperature and humidity of the air inside the biosphere in dynamic conditions and to interpret the experimental observations. The main findings of this research were: (i) the photosynthetically active radiation measured inside the underwater biosphere was 25–30% of that at sea level, (ii) the air temperature and relative humidity inside the biosphere showed cyclic daily variations that permitted a water evaporation/vapour condensation process, allowing the self-production of water for plant irrigation, and (iii) the results given by the lumped-parameter theoretical model were in a good agreement with the experiments
Accurate design of BHE fields for geothermal heat pump systems: The ASHRAE-Tp8 method compared to non aggregated schemes applied to different European test cases
No full textA Free Online Tool for the Design of Borehole Heat Exchanger Fields in Geothermal Heat Pump Applications at 10 and 25-Year Horizons
No full textExtending the ASHRAE method to a 25-year horizon through the Tp8 model for temperature penalty accurate estimation
No full textThe accurate design of Borehole Heat Exchangers (BHE) fields in ground-coupled heat pump (GCHP) systems is crucial for ensuring long-term performance. Traditional sizing methods, such as the ASHRAE method as modified by ASHRAE-Tp8 version, consider the annual building heating and cooling demand over a 10-year time horizon by applying the temporal superposition of 3 aggregated thermal pulses of different durations.
The present paper aims to clarify how the ASHRAE-Tp8 method could be adapted to be employed over a 25-year plant operation horizon. Temperature penalty estimations are compared with "real" precalculated temperature response factors (g-functions) through the minimization of a suitable objective function.
Optimized constants for the present new ASHRAE-Tp8 method are derived, enabling its easy adaptation for the 25-year time period. Comparisons with EED and GLHEPRO commercial software results demonstrate the reliability of this improved method, with borefield length estimations accurate within 7% and 6% respectively.
The results reported in the present paper lead to easily inferring the error in terms of overall length and borehole depth that would be obtained by employing the design process proper of the 10-year reference period when the 25-year time horizon is considered.
The methodology is in general demonstrated to be applicable to different time frames
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